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In this paper, the deformation behavior of a nickel-based single-crystal superalloy with [ 1 ¯ 40] and [ 3 ¯ 40] orientations was studied at room temperature by in situ electron backscattered diffraction (EBSD) tensile equipment. The mechanical properties, slip behavior and the corresponding Schmidt factor were analyzed. The deformation bands generated during the plastic deformation stage were found and characterized by using the electron backscattered diffraction (EBSD) technique. Furthermore, the formation and propagation of deformation bands played a softening effect on stress–strain curves; however, the secondary slip bands occurring after the propagation of deformation bands played a hardening effect. Finally, the formation of deformation band and its propagation on the mechanical properties are discussed. [ABSTRACT FROM AUTHOR]

Understanding the oxidation of Ni-based single crystal (SX) superalloys is significantly important because oxidation can damage the microstructure and eventually lead to failure of the alloy. Using advanced scanning/transmission electron microscopy, oxidation effects on the microstructure of a SX superalloy during heat treatment and simulated service (stress/temperature coupling) conditions are systematically investigated in order to reveal oxide microstructures and oxidation mechanisms. Heat treatment in argon results in less weight loss, thinner γ′-free layer and fewer internal oxidation than that treated in air. But the oxide layer structures and influence depths of oxidation in both atmospheres are similar. External tensile stress not only accelerates the oxidation of alloy but also affects the oxide microstructures. Moreover, stress effects on the oxidation microstructure depend on temperature. At 750 °C, Ni–Co oxides are formed on the alloy surface, followed by the inner layer of Ni–Co–Mo–Re–W oxides at the location of original γ phase under stress free condition. As the stress increases, an oxide layer mainly containing Al, Cr, Nb, Mo and Re elements is formed between the above two oxide layers. When temperature increases to 1050 °C, as applied tensile stress increases, the thickness of oxide layer increases but the structure of oxide layer is not obviously changed. [ABSTRACT FROM AUTHOR]

This study aimed to compare the dynamic microstructure evolution and the creep mechanical properties of second-generation nickel-based single-crystal superalloys at 780 °C/720 MPa and 850 °C/720 MPa. A method based on in situ scanning electron microscopy creep testing was used to identify the occurrence of slip bands. At the same time, the deformation mechanisms at 780 °C and 850 °C were discussed. The creep life at 780 °C was longer, almost five times that at 850 °C. Moreover, significant necking occurred in the primary creep at 780 °C, which controlled the entire creep process and accounted for almost 50% of the total life. In comparison, the primary creep at 850 °C was obviously shortened, mainly showing the characteristics of the second and third stages; the necking was mainly concentrated in the later stage of creep. This difference must be caused by the dislocation motion. The slip deformation mainly occurred at 780 °C, and the < 112 > dislocations shearing γ′ strengthening phase left obvious slip bands on the surface. The dislocations moved in the matrix channel in the early stage of creep at 850 °C, and the dislocations sheared γ′ strengthening phases in the later stage of creep while leaving obvious slip bands on the surface. [ABSTRACT FROM AUTHOR]

The effect of deformation temperature on tensile behavior of Inconel 718 alloy has been studied by a self-developed in-situ high-temperature tensile stage inside a scanning electron microscopy at a temperature range from room temperature (RT) to 750 °C. The dynamic microstructure evolution and mechanical properties at different temperatures were performed and compared by the uniaxial tensile tests. The in-situ test results showed that the mechanical properties and fracture mechanisms of Inconel 718 alloy were sensitive to deformation temperatures. From RT to 650 °C, the yield stress and ultimate tensile strength decrease slightly and the tensile ductility is comparable. While up to 750 °C, the yield stress and ultimate tensile strength decrease significantly, the elongation and reduction of cross section also showed a significant decrease from RT to 750 °C. It was found that at RT and 650 °C, tensile cracks tended to initiate around the carbide particles and the triple junctions of grain boundaries, also propagated transgranularly; at 750 °C, the cracks initiated at grain boundaries and propagated intergranularly. In fact, with the increase in deformation temperature, the fracture mechanism transformed from the ductile transgranular fracture to the brittle intergranular fracture. [ABSTRACT FROM AUTHOR]